How to get specific error message to Data Validation using Regex with python 3

How do i get a specific output like the below examples:

example 1 - If the user inputs Alberta, UN. I want to be able to see the print result as I'm sorry, UN is an invalid province abbreviation. I would love if the program can display an exact error in relation to user's input. Instead of an error saying I'm sorry this is an error, without any specific message to let the user know where his/her fault is.

I would really appreciate it if i could get some results, because i have been brainstorming on how to make it work

# Import
import re

# Program interface
print("====== POSTAL CODE CHECKER PROGRAM ====== ")
print("""
Select from below city/Province and enter it
--------------------------------------------
Alberta -  AB,
British Columbia - BC
Manitoba - MB
New Brunswick - NB
Newfoundland - NL
Northwest Territories - NT
Nova Scotia - NS
Nunavut - NU
Ontario - ON
Prince Edward Island - PE
Quebec -QC
Saskatchewan - SK
Yukon - YT
""")

# User input 1
province_input = input("Please enter the city/province: ")

pattern = re.compile(r'[ABMNOPQSYabcdefhiklmnorstuvw]| [CBTSE]| [I], [ABMNOPQSY]+[BCLTSUNEK]')

if pattern.match(province_input):
    print("You have successfully inputted {} the right province.".format(province_input))
elif not pattern.match(province_input):
    print("I'm sorry, {} is an invalid province abbreviation".format(province_input))
else:
    print("I'm sorry, your city or province is incorrectly formatted.")